Serine protease inactivated by freezing. Why? (fwd)

Hao Xiao haoxiao at cc.UManitoba.CA
Thu Feb 16 11:40:31 EST 1995

Mr. P.A. Sansom writes:
> From BIOSCI-REQUEST at Wed Feb 15 12:08:42 1995
> To: bioforum at
> From: psansom at (Mr. P.A. Sansom)
> Subject: Serine protease inactivated by freezing. Why?
> Date: 15 Feb 1995 17:52:01 -0000
> Sender: lpddist at
> Message-ID: <3htf01$2sm at>
> Original-To: bioforum at
> Hello Peeps!
> My monocyte membrane extracts contain a serine protease that loses activity on
> freezing at -20C, even though it's very stable at 4C. If the extract is left
> at 37C prior to assay, partial activity returns. This leads me to think that
> 1) the proteinase is a multi-subunit enzyme that breaks up and reforms or
> 2) an inactive form of the enzyme is converted to the active form at 37C.
> The enzyme is inhibited by PMSF but not by trypsin/chymotrypsin inhibitors.
> Has anyone experienced anything similar? I would really like to know what
> this enzyme is and if this effect has been seen with any other known enzyme
> eg elastase, gelatinase-like enzymes.
> Thanks in advance
> Paul
> psansom at
> Paul A Sansom                                  tel: 081-748-9966 x4208
> Department of Biochemistry                     fax: 081-748-5090
> The Kennedy Institute of Rheumatology
> 6 Bute Gardens
> Hammersmith
> London W6 7DW

I hardly believe that serine proteinase involvesa subunit since the sources 
of catalysis are ser-his-carboxylate triad. The loss of activity may 
be attributed to the conformational change. Just a speculation.

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